Abstract
Semiconductor nanocrystals are rapidly spreading into the display and lighting markets. Compared with liquid crystal and organic LED displays, nanocrystalline quantum dots (QDs) provide highly saturated colors, wide color gamut, resolution, rapid response time, optical efficiency, durability and low cost. This remarkable progress has been made possible by the rapid advances in the synthesis of colloidal QDs and by the progress in understanding the intriguing new physics exhibited by these nanoparticles. In this review, we provide support to the idea that suitably engineered core/graded-shell QDs exhibit exceptionally favorable optical properties, photoluminescence and optical gain, while keeping the synthesis facile and producing QDs well suited for light emitting applications. Solid-state laser emitters can greatly profit from QDs as efficient gain materials. Progress towards fabricating low threshold, solution processed DFB lasers that are optically pumped using one- and two-photon absorption is reviewed. In the field of display technologies, the exploitation of the exceptional photoluminescence properties of QDs for LCD backlighting has already advanced to commercial levels. The next big challenge is to develop the electroluminescence properties of QD to a similar state. We present an overview of QLED devices and of the great perspectives for next generation display and lighting technologies.
Highlights
Liquid crystal displays (LCD) and organic light emitting diodes (OLED) are the two major technologies competing within the $100 bn display market [1], each with its own advantages and disadvantages
LCD is leading in lifetime, power consumption, resolution density and cost; comparable to OLED in ambient contrast ratio and viewing angle, but inferior in such fundamental requirements as color and brightness, module thickness/flexibility and response time [1,2,3]
Materials 2016, 9, 672 used either exploiting their photoluminescence for LCD backlight unit or their electroluminescence for quantum dots (QDs)-light emitting diodes (QLED). Advances in this display technology are expected from the development of QD-based light emitting diodes (QLED) currently underway [7,8]. This remarkable progress has been made possible by the rapid advances in the synthesis of colloidal QDs and by the progress in understanding the intriguing new physics exhibited by these nanoparticles and how it relates to their structure [9,10]
Summary
Liquid crystal displays (LCD) and organic light emitting diodes (OLED) are the two major technologies competing within the $100 bn display market [1], each with its own advantages and disadvantages. QDs possess sufficiently strong light absorption properties and/or efficient and stable emission to be considered superior compared to molecular organic dyes These features, including one- and two-photon absorption, are direct consequences of the quantum confinement effect and of the atom-like density-of-states of excitons at moderate energies above the bulk energy gap of the constituent semiconductor material. Compositional engineering of the core/shell structure can favor preferential charge separation through a Type-II configuration (for example: CdTe/CdSe, CdSe/ZnTe, InP/CdS) [31,32,33] (see Figure 1b,c) Such a structure provides control of the spatial overlap between electrons and holes; enabling a facile way to manipulate Coulomb interactions in nanostructures. This is important for developing efficient light emitting devices, non-linear optical applications and photovoltaics [29].
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